Atherosclerosis and the resulting cardiovascular disease (CVD) are the leading cause of mortality in the United States of America where one in every three deaths is attributed to CVD. Risk factors such as ageing, obesity, smoking and hypertension have been identified but the cause of the atherosclerosis is still unknown. Increased production of reactive oxygen species (ROS) and telomere dysfunction has been implicated in the development of atherosclerosis. ROS is considered a significant contributor to CVD and there is increased occurrence of shorten telomeres in atherosclerotic plaques. Additionally, shortened telomeres in leucocytes are associated with increased pre-disposition of CVD. Recently published reports have identified ROS as a regulator of TERT, the catalytic subunit of telomerase, which uses its enzymatic activity to maintain telomere length. The newly discovered relationship between ROS and TERT suggests that their roles in CVD are interconnected. However, the relationship between ROS and telomere maintenance in CVD progression is poorly understood, and it is not clear whether the relationship is causative or correlative. I hypothesize that the pro-atherosclerotic effects of ROS are in part the result of ROS action on telomere function. Here, I propose a series of studies to determine the effects of increased oxidative stress on telomere maintenance. For this proposal, I will utilize the aortic smooth muscle cells (SMCs) isolated from haplodeficient superoxide dismutase 2 (SOD2 ) mice, an established model used to study ROS contribution to atherosclerosis. This innovative use of SOD2 mouse allows me to directly assess telomere and telomerase status in an atherosclerotic model. For Aim 1, I will determine ROS effect on telomerase activity and the mechanisms of ROS regulation of telomerase. Preliminary data shows that telomerase activity is approximately 50% less in SOD2 SMCs compared to wild type (WT) SMCs confirming that increased oxidative stress decreases telomerase activity. In Aim 2, I will determine the effects of ROS on telomeres by measuring telomere lengths and telomere integrity. In Aim 3, I will determine if the anti-atherosclerotic agents estrogen and vitamin E reverse ROS-dependent deficits in telomere maintenance. The results from these studies will provide the basis for understanding ROS regulation of TERT in vivo (Aim 1), provide a direct assessment of the effects of ROS on telomeres (Aim 2) and determine if telomere maintenance is a target of anti-atherosclerotic agents (Aim3). Overall, the completion of the proposed research will elucidate a direct connection between ROS and telomere maintenance in CVD mechanism furthering our goal to form an accurate and complete understanding of the molecular basis of atherosclerosis. Increased understanding of CVD molecular mechanisms will improve strategies towards the treatment, prevention and diagnosis of CVD.